1. Field of the Invention
The invention relates to a method of using wheel alignment apparatus to produce more accurate information about wheel alignment by cooperative coupling of the apparatus to compensate the same and substantially eliminate undesired effects present in the rotational response of the wheels and in the attachment of the apparatus to the wheels.
2. Description of the Prior Art
It is recognized that the alignment of the wheels of a vehicle contributes greatly to its safe operation on the streets and highways. Many different types of apparatus have been provided for diagnosing wheel alignment characteristics. Since there may be errors present in the way the respective vehicle wheels rotate, and since the alignment apparatus may introduce additional errors due to the way the mounting thereof on the wheels is made, it is important to compensate for such errors so as to improve the accuracy in wheel alignment diagnostic results.
There are believed to be three general classes of wheel alignment apparatus, and the prior art may be conveniently placed in those groups.
The least pertinent class relates to the measurement of toe-in characteristics of the steerable wheels, without regard to other wheels. This class typically comprises prior art disclosures found in Bender U.S. Pat. Nos. 2,532,593 of Dec. 5, 1950; MacMillan 3,135,052 of June 2, 1964; MacMillan 3,393,455 of July 23, 1968; Wilkerson 3,426,438 of Feb. 11, 1969; MacMillan 3,443,318 of May 13, 1969; German Offenlegungsschrift No. 1,548,203 of Sept. 25, 1969; Butler 3,865,492 of Feb. 11, 1975; and Senften 4,034,479 of July 12, 1977.
There is a class of prior art in which the main consideration is the toe alignment of steerable wheels, but the relationship of the steerable wheels to the position of the non-steerable wheels is considered to some extent. This class includes prior art patents of Holub U.S. Pat. Nos. 2,972,189 of Feb. 21, 1961; Manlove 3,164,910 of Jan. 12, 1965; Holub 3,337,961 of Aug. 29, 1967; Rishovd et al 3,963,352 of June 15, 1976; Florer et al 4,095,902 of June 20, 1978; Lill 4,097,157 of June 27, 1978; Hunter 4,106,208 of Aug. 15, 1978; and Roberts et al 4,150,897 of Apr. 24, 1979.
Finally the prior art class which has disclosed alignment equipment in which the non-steerable wheel positions have been considered with the positions of the steerable wheel includes Carrigan 2,601,262 of June 24, 1952; Manlove 3,181,248 of May 4, 1965; and Senften 4,126,943 of Nov. 28, 1978.
In addition to the foregoing prior art in the last class, there are more recent patents dealing in some measure with electronic methods for effecting compensation for wheel runout. These are Senften 3,892,042 of July 1, 1975 and Chang 4,192,074 of Mar. 11, 1980. Chang has recognized the teaching of Senften and has carried it into a system for continuously generating inclination signals pertaining to the steerable wheel toe and camber relationships.